This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/DE00/02507 which has an International filing date of Jul. 28, 2000, which designated the United States of America, the entire contents of which are hereby incorporated by reference.
The present invention generally relates to a tripping delay circuit for an electromechanical switching device. Preferably, it relates to one wherein two input terminals are included, via which the tripping delay circuit can be fed an input voltage, and two output terminals, via which a supply voltage can be applied to the switching device. The output terminals may be connected to each other via an energy storage mechanism, the energy storage mechanism allowing a dip in the input voltage to be bridged, at least for a short time. The switching device may change its switching state when the supply voltage falls below a withstand voltage.
A tripping delay circuit of this type is generally known. DE 32 39 840 C2 is cited by way of example.
During the tripping of an electromagnetic switching device (contactor or relay), it may happen that, although the switching device initially drops out when the voltage falls below its withstand voltage, it then briefly reverses its direction of movement again or at least drops out considerably more slowly. This may lead to increased contact wear in the switching device. Furthermore, effects on a load switched by the switching device may occur.
An object of the present invention is to design a tripping delay circuit. Preferably it is designed in such a way that a quick, reliable switching of the switching device takes place when the switching state changes due to falling of the supply voltage.
An object is achieved by a tripping delay circuit having a voltage-sensitive switching element. Preferably, it is one which separates the energy storage mechanism from the output terminals when the supply voltage falls below a limiting voltage, the limiting voltage being greater than the withstand voltage.
This can occur because, as a result, when the supply voltage falls, an energy supply to the switching device is completely interrupted even before the withstand voltage is reached, so that said device drops out quickly and with certainty.
If the limiting voltage is adjustable, the tripping delay circuit can be used universally for different electromechanical switching devices.
Preferably, the supply voltage has a nominal voltage and the output terminals are connected to each other via an overvoltage protection element, which becomes current-conducting if an overvoltage which is greater than the nominal voltage drops across it. This is so because, as a result, an effective overvoltage protection for the connected switching device takes place on the one hand, and the magnetic energy stored in the switching device is quickly transformed into heat on the other hand.
If the output terminals are connected to the input terminals, the voltage-sensitive switching element is preferably arranged in such a way that it separates one of the input terminals from one of the output terminals. It is also possible, however, for it to be arranged in such a way that is separates only the energy storage mechanism from the output terminals.
The energy storage mechanism may be designed for example as a storage capacitor with which a charging resistor is connected in series.
The voltage-sensitive switching element may be designed for example as a relay with a Zener diode connected in series.
Alternatively, the voltage-sensitive switching element may be designed as a semiconductor switch.